In frozen display cases and particularly those used in commercial establishments such as supermarkets, a portion of the display case is left open for displaying the items for sale and providing access to these items for the consumers. These types of refrigerators are typically known as an open front upright refrigerator or open top coffin refrigerators. An example of the former appears in copending application Ser. No. 764,157 entitled "ROLL IN OPEN FRONT FROZEN FOOD REFRIGERATOR CASE"; an example of the latter is shown in U.S. Pat. No. 3,425,236 to Streed et al. In both of these refrigerators, an air curtain or band is employed across the open portion of the refrigerator to maintain the interior portion of the case where the frozen foods are displayed insulated from the ambient air on the outside of the refrigerator.
However, in using such air bands at least one air band will be substantially colder than the ambient air. As the band travels across the opening of the freezer, some of this ambient air may be mixed with the cold air band and deposited on the discharge and receiving openings on the ducts which provide the path for the air band.
In the receiving duct opening, a grill and liquid refrigerant coils have been provided to heat the grill sufficiently above the dew point thereby avoiding an accumulation of frost on the return grill. However, it is usually not feasible at the discharge opening of the duct to include such coils within the grill structure. This is because the grill may unnecessarily block the air flow path creating additional pressure drops which results in a need for a larger horsepower fan to force the air through the grill and coil structure. With regard to the cold air band, the whole purpose of the use of the air band will be defeated if it is heated as it leaves the discharge opening. As a result, although frost can be eliminated on the return grill, the discharge openings are not readily susceptible to the same kind of construction as the return opening. As a result, the moisture carried by the ambient air may crystallize on portions of the duct adjacent the discharge opening for the cold air. If this process is allowed to continue, frost may accumulate to such an extent that the cold air band will be diverted from its normal flow path thereby defeating the purpose of insulating the interior of the case. Also, there may be blockage of the discharge opening creating an adverse effect on the flow rate of the cold air band. Beyond these problems, there is also simply the unsightly appearance of large amounts of frost over operating portions of a refrigeration unit in a commercial establishment.
It is an object of the present invention to provide a means for heating areas of ducts adjacent the discharge opening for preventing the accumulation of frost thereon and its concomitant adverse effect on the flow path of the air band.
It is a further object of the invention to provide a separator between two discharge openings for separating air bands of different temperatures and maintaining the separator at a temperature above the dew point to prevent the accumulation of frost and ensure proper separation of the air bands.
It is a further object of the invention to utilize a portion of the return conduits of refrigeration systems for raising the temperature of the duct adjacent discharge openings on open front or open top refrigerators sufficiently above the dew point to avoid the accumulation of frost.
It is also an object of the invention to locate heating means adjacent the opening of a discharge duct for an air band to prevent the accumulation of frost without unnecessarily heating of the air band.
It is a further object of the invention to employ a system for heating areas of a freezer.
It is a further object of the invention to employ a system for heating areas of a freezer adjacent the opening of a discharge duct which simultaneously enhances the efficiency of refrigeration systems used in cooling the case to a desired temperature.
It is an additional object of the invention to provide a portion of refrigerant lines in both the discharge ducts and return ducts for the prevention of frost in areas on or adjacent these openings and simultaneously subcooling the liquid refrigerant carried in the lines thereby enhancing the efficiency of the refrigeration system.
This invention accomplishes the above and other objects in the following manner.